<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <div id="app">
        <span v-if="isUser">
            <label for="username">用户账号</label>
            <input type="text" id="username" placeholder="用户账号" key="username">
        </span>
        <span v-else>
            <label for="email">用户邮箱</label>
            <input type="text" id="email"  placeholder="用户邮箱"  key="email">
        </span>
        <button @click="isUser = !isUser">切换类型</button>
    </div>
    <script src="../js/vue.js"></script>
 <script>
        const app=new Vue({
            el:'#app',
            data:{
                isUser: true,
            }
        })
    </script>
</body>
</html>